The temperature of the fuel cell stack portion of a PEM fuel cell power plant is regulated by a coolant stream which absorbs heat from the cells in the stack. In PEM type fuel cell power plants that utilize porous plate water transfer elements which are directly exposed to the liquid coolant, the coolant will also will entrain gas bubbles which are derived from the porous water transfer plates as the coolant stream passes through the cell stack area of the power plant. U.S. Pat. No. 5,503,944 dated Apr. 2, 1996, which is incorporated herein in its entirety, discloses a PEM fuel cell power plant which includes porous water transfer plates which absorb water that is formed on the cathode side of the electrolyte membranes in the fuel cells. The absorbed water passes through the porous plates and enters the circulating coolant stream which is used to control the temperature of the cells. The cathode water also includes air bubbles that are passed through the porous plates and thus enter the coolant stream. A similar phenomenon on the anode side causes gaseous fuel constituents to pass through its porous water transfer plate. Since the coolant stream is constantly recycled through the fuel cell stack, the amount of gas entrained in the coolant stream will increase with time. The resultant build up of gas bubbles which are entrained in the coolant stream will adversely affect the cooling capacity of the coolant stream. Entrained gas bubbles also adversely affect the ability of the coolant pump to recirculate the coolant liquid by forming a two phase mixture in the coolant liquid thereby rendering the coolant liquid difficult to pump. Therefore, the gas bubbles should be removed from the coolant stream during the recycling of the coolant stream in the power plant in order to maintain the ability of the coolant stream to regulate the operating temperature of the power plant. Separating the gas bubbles from the coolant liquid will also allow the use of simpler, lower cost, longer life coolant recirculation pumps with a net positive suction head, such as a centrifugal type pump.